1. Field of the Invention
The present invention relates to improved continuous loop reactors. More specifically, the invention relates to reactors defining a spiral three-dimensional flow pattern such that the flow pattern affords time for separations and/or completion of reactions.
2. Description of the Prior Art
Continuous Loop Reactors have been predominantly used in sewage treatment. These require a loop, usually a long channel joined end to beginning so as to provide continuous cycle flow. These traditionally use a directional flow at a minimum velocity of about two feet per second to prevent separation by sedimentation of components of the fluid; sludge and water. Reagents are added at particular sites and reactions occur in time along particular zones of the flow channel as the reagents react.
Processes for treating and denitrifying fermented waste water are well known. In a fermentation process, proteins are converted predominantly to ammonia and organic acids, and carbohydrates are predominantly converted to organic acids. Fermentation can be considered a preconditioning step to further treatment. In a popular process using an oxidative ditch, a particular type of continuous loop reactor, fermented waste is treated and denitrified simultaneously. In this continuous loop reactor, oxygen may be added to fluid fermented waste at a particular site. The fluid, fermented waste water and microbe rich suspension, is aerobic when it contains dissolved oxygen (O.sub.2) from the air. Microbes use the oxygen to procreate and to convert some of the ammonia to nitrite and then nitrate. In the course of procreation and metabolism, they consume some organic acids.
Dissolved O.sub.2 is consumed as the flow continues along the loop in an environment rich in oxygen consuming microbes, organic acids, and ammonia. Some point along the loop, the dissolved O.sub.2 is totally consumed. At this point, and for some further distance downstream along the loop, there are nitrates from bio-oxidation of the ammonia dissolved in the fluid. Since the microbes in the fluid still have a demand for oxygen, they then use the nitrate as a source of oxygen, converting the nitrates to nitrogen gas (N.sub.2), most of which is liberated. In a condition wherein available oxygen is in a form other than O.sub.2, for example nitrate, the fluid is considered to anoxic.
The microbes are sustained on nitrate until air containing O2 is again added to the fluid. The flow cycle and addition of reagents continue as the organic acids and ammonia are incorporated in the sludge as an increased population of microbes, or as the organic acids and ammonia are converted to H.sub.2 O, Co.sub.2, and N.sub.2. Phosphorous and minerals are components of the sludge. Thus, by treating fermented waste water in a reactor that enables the separation of the aerobic zone and anoxic zone, the components that contaminate waste water are removed as sludge and harmless chemicals H.sub.2 O, CO.sub.2, and N.sub.2.
Fermented waste water is usually added at a point just before the flow becomes anoxic. At this point, the fresh addition of organic acids from the fermented sewage stimulates the microbes' metabolism to consume nitrate.
Predominantly in the existing art, treated waste water is normally withdrawn from the continuous loop reactor just after aeration. At this phase, phosphorous present is mostly attached to the sludge, and the sludge tends to settle easily. Withdrawn aerated water may be sent to a clarifier. The microbes settle to the reactor's bottom as sludge. Some percentage of the sludge may be withdrawn and returned to the continuous loop reactor. The returned sludge maintains a high microbe density. This high density enables a more intense treatment per unit volume of reactor when compared to reactors without such a return. The remainder of the sludge is withdrawn and disposed of in any appropriate manner.
Clarified water from which sludge is removed is reduced in contaminants. Among contaminants reduced are proteins and carbohydrates which may exist in various stages of decomposition prior to fermentation.
In processes like the above, three containments are typically used:
(A) A fermentation tank to precondition sewage; PA1 (B) A continuous loop reactor to treat and dinitrify fermented sewage which allows separated and sequenced reactions to take place without sedimentation of sludge in the loop of flow; and PA1 (C) A clarifier to clarify treated waste water, recover some useful sludge for return to the continuous loop reactor, and to concentrate sludge for disposal.
Traditionally, oxidative ditches for denitrification and purification are configured as a loop. The loop may be in the form of circle, a narrow ellipse, or a folded narrow ellipse. The flow in these conventional oxidative ditches is lateral, as the loop is defined substantially in a horizontal plane. In oxidative ditches, the loop must be long enough such that the time provided by the flow over its length is sufficient for both aerobic and anoxic stages to proceed. In an oxidative ditch loop, induced minimum flow velocity must be such that all wetted surfaces are prevented from accumulating sediment. Sediments will produce foul smelling gases as undesirable anaerobic pockets results. These anaerobic pockets of decaying settled sludge also decrease the denitrification efficiency by wastefully producing methane gas from organic acids. An excess of organic acids usually drives the denitrification step to near completion. Usually a minimum flow velocity is required substantially along the entire loop, typically of about 2 feet per second. Typically, the minimum time for a flow sequence (aeration to aerobic to anoxic) to be effective is about eight minutes. Accordingly, loops of about 480 feet, as described in U.S. Pat. No. 4,146,478 are common. This lengthy flow path makes traditional continuous loop reactors used in denitrification very extensive devices regardless of the volume of sewage being treated.
Further, since most loops include bends, folds, and sharp turns, auxiliary flow motivation and/or vanes are usually required to maintain this minimum flow velocity over all horizontal wetted surfaces to prevent sedimentation. The prior art includes several patents directed to maintaining and/or controlling flow velocities. For example, U.S. Pat. No. 4,278,547 issued Jul. 14, 1981 and U.S. Pat. No. 4,902,302 issued Feb. 20, 1990, both to Reid describe combinations of dual baffle aerators and barriered pump/directional mix jet aerators to conserve momentum of flow in an oxidative ditch. U.S. Pat. No. 4,460,471, issued Jul. 17, 1984 describes flow-control turbines in a barrier type oxidative ditch. U.S. Pat. No. 5,118,415 issued Jun. 2, 1992 to Weis et al. describes an oxidative ditch velocity control system that includes turning baffle members in the end sections of the flow channel. U.S. Pat. No. 4,869,818 issued Sep. 26, 1989 to DiGregorio et al. describes radial flow impellers to enhance propulsion of mixed liquor along the bottom of an oxidative ditch, thereby allowing deeper ditches to be used.
While effective in treating waste waters, several disadvantages exist in oxidative ditch loops. Among these, the loop length required for an oxidative ditch to be effective requires relatively flat land of sufficient area to allow both aerobic and anoxic stages to proceed. Materials for lining walls and floors of long loops (including concrete and/or rubber) can become cost prohibitive. Additionally, the high air to water surface area in a standard oxidative ditch is an undesirable source of oxygen in the anoxic stage of the process. Further, energy demands to provide aeration and flow motivation reduces the overall efficiency of standard oxidative ditch systems.
In addressing the land area problem, U.S. Pat. No. 4,146,478 describes a substantially horizontal, closed spiral path waste water treating system in which concentric loops are rigidly defined by walls. Though this structure does save land area by compact horizontal design, a lengthy flow path is still defined by specifically constructed walls, and the same minimum flow velocity typically used to prevent sedimentation still applies. Similarly, U.S. Pat. No. 4,975,197 describes an orbital type apparatus having concentric channels in which waste water may flow from one channel into an adjacent channel. Though land area use is reduced in these types of oxidative ditches, construction material used in defining plural small channels is proportionally higher when taking into account reduced channel flow capacities. Further, efficiency is reduced as greater friction at walls is encounter per unit volume of waste water treated.
To reduce air to water surface contact during the anoxic stage, U.S. Pat. No. 5,234,595 issued Aug. 10, 1993 to DiGregorio et al. describes an oxidative orbital treatment system that includes an aerobic zone and an anoxic zone, arranged one on top of the other. The zones are separated by an imperforate baffle provided under a surface aerator. U.S. Pat. No. 4,455,232 issued Jun. 19, 1984 to Reid describes eddy jet diffusers for aerating induced flow with improved oxygen transfer efficiencies. U.S. Pat. No. 5,582,734 describes automated determination of nitrogen depletion and improved total nitrogen removal using a control system to increase efficiency.
None of the above inventions and patents, taken either singly or in combination, is seen to describe the instant invention as claimed.